external-secrets/Spec.md

```yaml
---
title: Standardize ExternalSecret CRD
authors: all of us
creation-date: 2020-09-01
status: draft
---
```

# Standardize ExternalSecret CRD

## Table of Contents

<!-- toc -->
- [Summary](#summary)
- [Motivation](#motivation)
  - [Goals](#goals)
  - [Non-Goals](#non-goals)
- [Terminology](#terminology)
- [Use-Cases](#use-cases)
- [Proposal](#proposal)
  - [API](#api)
- [Alternatives](#alternatives)
<!-- /toc -->

## Summary

This is a proposal to standardize the `ExternalSecret` CRD in an combined effort through all projects that deal with syncing external secrets. This proposal aims to do find the _common denominator_ for all users of `ExternalSecrets`.

## Motivation

There are a lot of different projects in the wild that essentially do the same thing: sync secrets with Kubernetes. The idea is to unify efforts into a single project that serves the needs of all users in this problem space.

As a starting point i would like to define a **common denominator** for a CustomResourceDefinition that serves all known use-cases. This CRD should follow the standard alpha -> beta -> GA feature process.

Once the CRD API is defined we can move on with more delicate discussions about technology, organization and processes.

List of Projects known so far or related:
* https://github.com/godaddy/kubernetes-external-secrets
* https://github.com/itscontained/secret-manager
* https://github.com/ContainerSolutions/externalsecret-operator
* https://github.com/mumoshu/aws-secret-operator
* https://github.com/cmattoon/aws-ssm
* https://github.com/tuenti/secrets-manager
* https://github.com/kubernetes-sigs/k8s-gsm-tools

### Goals

- Define a alpha CRD
- Fully document the Spec and use-cases

### Non-Goals

This KEP proposes the CRD Spec and documents the use-cases, not the choice of technology or migration path towards implementing the CRD.

We do not want to sync secrets into a `ConfigMap`.

## Terminology

* Kubernetes External Secrets `KES`: A Application that runs a control loop which syncs secrets
* KES `instance`: A single entity that runs a control loop.
* ExternalSecret `ES`: A CustomResource that declares which secrets should be synced
* Store: Is a **source** for secrets. The Store is external to KES. It can be a hosted service like Alibabacloud SecretsManager, AWS SystemsManager, Azure KeyVault...
* Frontend: A **sink** for the synced secrets. Usually a `Secret`
* Secret: credentials that act as a key to sensitive information

## Use-Cases
* one global KES instance that manages ES in **all namespaces**, which gives access to **all stores**, with ACL
* multiple global KES instances, each manages access to a single or multiple stores (e.g.: shard by stage or team...)
* one KES per namespace (a user manages his/her own KES instance)

### User definitions
* `operator :=` i manage one or multiple `KES` instances
* `user :=` i only create `ES`, KES is managed by someone else

### User Stories
From that we can derive the following requirements or user-stories:
1. AS a KES operator i want to run multiple KES instances per cluster (e.g. one KES instance per DEV/PROD)
2. AS a KES operator or user i want to integrate **multiple stores** from a **single KES instance** (e.g. dev namespace has access only to dev secrets)
3. AS a KES user i want to control the sink for the secrets (aka frontend: store secret as `kind=Secret`)
4. AS a KES user i want to fetch **from multiple** stores and store the secrets **in a single** Frontend
5. AS a KES operator i want to limit the access to certain stores or subresources (e.g. having one central KES instance that handles all ES - similar to `iam.amazonaws.com/permitted` annotation per namespace)
4. AS a KES user i want to provide an application with a configuration that contains a secret

### Stores

These stores are relevant:
* AWS Secure Systems Manager Parameter Store
* AWS Secrets Manager
* Hashicorp Vault
* Azure Key Vault
* Alibaba Cloud KMS Secret Manager
* Google Cloud Platform Secret Manager
* Kubernetes (see #422)
* noop (see #476)

### Frontends

* Kind=Secret
* *potentially* we could sync store to store

## Proposal

### API

### External Secret

The `ExternalSecret` CustomResourceDefinition is **namespaced**. It defines the following:
1. source for the secret (store)
2. sink for the secret (fronted)
3. and a mapping to translate the keys

```yaml
apiVersion: external-secrets.k8s.io/v1alpha1
kind: ExternalSecret
metadata: {...}

spec:

  # the amount of time before the values will be read again from the store
  # may be set to zero to fetch and create it once
  refreshInterval: "1h"

  # there can only be one target per ES
  target:
    # The secret name of the resource
    # defaults to .metadata.name of the ExternalSecret. immutable.
    name: my-secret

    # Enum with values: 'Owner', 'Merge', or 'None'
    # Default value of 'Owner'
    # Owner creates the secret and sets .metadata.ownerReferences of the resource
    # Merge does not create the secret, but merges in the data fields to the secret
    # None does not create a secret (future use with injector)
    creationPolicy: 'Merge'

    # specify a blueprint for the resulting Kind=Secret
    template:
      type: kubernetes.io/dockerconfigjson # or TLS...

      metadata:
        annotations: {}
        labels: {}

      # use inline templates to construct your desired config file that contains your secret
      data:
        config.yml: |
          endpoints:
          - https://{{ .data.user }}:{{ .data.password }}@api.exmaple.com

      # Uses an existing template from configmap
      # secret is fetched, merged and templated within the referenced configMap data
      # It does not update the configmap, it creates a secret with: data["alertmanager.yml"] = ...result...
      templateFrom:
      - configMap:
          name: alertmanager
          items:
          - key: alertmanager.yaml

  # data contains key/value pairs which correspond to the keys in the resulting secret
  data:

    # EXAMPLE 1: simple mapping
    # one key from a store may hold multiple values
    # we need a way to map the values to the frontend
    # it is the responsibility of the store implementation to know how to extract a value
    tls.crt:
      key: /corp.org/dev/certs/ingress
      property: pubcert
    tls.key:
      key: /corp.org/dev/certs/ingress
      property: privkey

  # used to fetch all properties from a secret.
  # if multiple dataFrom are specified, secrets are merged in the specified order
  dataFrom:
  - key: /user/all-creds

status:
  # represents the current phase of secret sync:
  # * Pending | ES created, controller did not yet sync the ES or other dependencies are missing (e.g. secret store or configmap template)
  # * Syncing | ES is being actively synced according to spec
  # * Failing | Secret can not be synced, this might require user intervention
  # * Failed  | ES can not be synced right now and will not able to
  # * Completed | ES was synced successfully (one-time use only)
  phase: Syncing
  conditions:
  - type: InSync
    status: "True" # False if last sync was not successful
    reason: "SecretSynced"
    message: "Secret was synced"
    lastTransitionTime: "2019-08-12T12:33:02Z"
    lastSyncTime: "2020-09-23T16:27:53Z"

```

#### Behavior

The ExternalSecret control loop **ensures** that the target resource exists and stays up to date with the upstream provider. Because most upstream APIs are limited in throughput the control loop must implement some sort of jitter and retry/backoff mechanic.

### External Secret Store

The store configuration in an `ExternalSecret` may contain a lot of redundancy, this can be factored out into its own CRD.
These stores are defined in a particular namespace using `SecretStore` **or** globally with `GlobalSecretStore`.

```yaml
apiVerson: external-secrets.k8s.io/v1alpha1
kind: SecretStore # or ClusterSecretStore
metadata:
  name: vault
  namespace: example-ns
spec:

  # optional.
  # used to select the correct KES controller (think: ingress.ingressClassName)
  # The KES controller is instantiated with a specific controller name
  # and filters ES based on this property
  controller: "dev"

  store:
    type: vault
    parameters: # provider specific k/v pairs
      server: "https://vault.example.com"
      path: path/on/vault/store
    auth: {} # provider specific k/v pairs

status:
  # * Pending: e.g. referenced secret containing credentials is missing
  # * Running: all dependencies are met, sync
  phase: Running
  conditions:
  - type: Ready
    status: "False"
    reason: "ErrorConfig"
    message: "Unable to assume role arn:xxxx"
    lastTransitionTime: "2019-08-12T12:33:02Z"
```

Example Secret that uses the reference to a store
```yaml
apiVersion: external-secrets.k8s.io/v1alpha1
kind: ExternalSecret
metadata:
  name: foo
spec:
  storeRef:
    kind: SecretStore # ClusterSecretStore
    name: my-store
  target:
    name: my-secret
    template:
      type: kubernetes.io/TLS
  data:
    tls.crt:
      key: /corp.org/dev/certs/ingress
      property: pubcert
    tls.key:
      key: /corp.org/dev/certs/ingress
      property: privkey
```

Workflow in a KES instance:
1. A user creates a Store with a certain `spec.controller`
2. A controller picks up the `ExternalSecret` if it matches the `controller` field
3. The controller fetches the secret from the provider and stores it as kind=Secret in the same namespace as ES


## Backlog

We have a bunch of features which are not relevant for the MVP implementation. We keep the features here in this backlog. Order is not specific:

1. Secret injection with a mutating Webhook [#81](https://github.com/godaddy/kubernetes-external-secrets/issues/81)